1. Field of Invention
The present invention generally relates to the art of microscopy, and more particularly to a three-dimensional optical microscope for multi-scale deformation and shape measurement.
2. Background and Related Art
Three-dimensional (3D) full-field deformation and morphology analyses are widely used in many industrial and research applications. Driven by advances in biology and nanotechnology, there is a growing need for performing such analyses at the micro-scale. A good example in point is the study of deformation and failure mechanisms of complex material systems. Detailed experimental full-field characteristics, in combination with theoretical and/or computational modeling, can provide crucial information in helping establish their microstructure-property relationships.
There are a range of optical techniques for measuring height profiles and displacements in 3D. Existing optical surface-profiling techniques can be divided into two categories: spatial-scanning methods and full-field methods.
The first category includes scanning-laser confocal microscopy, chromatic depth scanning method, and laser spot scanning or line scanning approaches. All of these methods are intrinsically point-wise or line-wise scanning methods, but can achieve full-field measurement by means of spatial scanning.
In the second category of inherent full-field methods, topographic reconstruction is done by processing two-dimensional (2D) optical images. Some of the commonly used full-field methods include white light and laser interferometry, projection Moire interferometry, depth from focus/defocus (DFF/DFD), as well as 3D digital image correlation (DIC). In general, the full-field methods allow much faster 3D topographic imaging than the spatial-scanning methods.
A small number of approaches are available for 3D full-field surface displacement measurement. Among them, electronic speckle pattern interferometry (ESPI) offers the highest sensitivity, but suffers from very limited measurement range due to speckle decorrelation. In recent years, 3D-DIC is being increasingly used for 3D deformation characterization for its ease of operation.
Despite the advent of the above measurement techniques, high-accuracy 3D surface deformation and profile characterizations at the micro-scale, however, remain a great challenge. Traditional optical microscopes can achieve sub-micron spatial resolution, but they are only capable of 2D imaging. In a recent study, a freeform prism array was developed that could be attached to the objective of a microscope to enable 3D stereo imaging. It demonstrated the viability of the method through quantitative 3D imaging tests, but did not provide an imaging processing algorithm for quantitative 3D shape reconstruction.
An image correlation-based technique, named diffraction assisted image correlation (DAIC), for 3D full-field deformation and profile measurement, is also known. The DAIC method utilizes a transmission grating and a single camera to achieve 3D perception, making it particularly suitable for both macroscopic and microscopic measurements.
Driven by a growing need in the fields of biomechanics and micro- and nano-mechanics research, non-contact full-field deformation characterization at micro-scale is gaining prominent significance, but has yet been satisfactorily achieved. While the traditional 3D-DIC combined with a stereo microscope has shown the capability to measure 3D deformation with micro-scale spatial resolution, the application of this technique to smaller length scales is hindered by the low-magnification power of stereo microscopy.
Therefore, there is a need for a 3D deformation measurement method with sub-micron spatial resolution. It is to the provision of such a system and method that the present invention is primarily directed.